This invention relates to a surface blasting product.
In mining and excavation processes, underground and on surface, there are, inevitably, boulders and rocks which can be difficult to handle because they have not been sufficiently fragmented during a primary blast or a caving step, or which may have been displaced from non-blasted areas. Secondary blasting techniques or impact devices can be used to reduce the sizes of these materials.
Secondary blasting methods are described in general in the specification of U.S. Pat. No. 5,233,926. An example of a secondary blasting charge is given in U.S. Pat. No. 2,247,169.
Rocks which are on the ground can, with a reasonable degree of safety, be broken using non-explosive or explosive techniques or impact hammers. When the rocks are overhead, for example if rocks in a chute or box hole form a blockage, then blasting of the rocks to eliminate the blockage can be, at best, problematic and, at worst, highly dangerous.
If the problem can tackled from above the blockage then a relatively large quantity of explosive could be required. In this event the energy which is released can be destructive to a structure which defines a passage in which the rock is located.
U.S. Pat. No. 5,233,926 describes the use of a shaped secondary blasting charge which contains a viscous adhesive explosive. In one example the charge is supported on a pole which is manipulated to allow the explosive charge to be adhesively bonded to a rock. This process can be carried out with a reasonable degree of safety. For a variety of reasons though the use of explosive material which is adhesive is not always successful, practical, nor desirable.
U.S. Pat. No. 2,247,169 describes a surface blasting shell in which a base flange on a capsule is coated with an adhesive to allow the capsule to be adhered to a rock to be blasted. This patent does not however describe a safe technique for using the blasting shell in an overhead application.
An object of the present invention is to provide a blasting product which can be used in a controlled manner with a substantial degree of safety to fragment or displace rock at an overhead location, while limiting the quantity of energy which is released, or otherwise directing the energy which is released, so that the likelihood of damage being caused to supporting structure is reduced.